Process for the preparation of a glass-ceramic blank for dental purposes

Abstract

The invention relates to a process for the preparation of a glass-ceramic blank for dental purposes with lithium silicate as crystal phase, in which lithium silicate blanks that are no longer required and in particular residues thereof are used as starting material and which allows the production of a homogeneous starting glass within a short time.

The invention claimed is: 
     
       1. Process for the preparation of a glass-ceramic blank for dental purposes with lithium silicate as crystal phase, comprising
 (a) lithium silicate blanks with different chemical composition or residues of lithium silicate blanks with different chemical composition are melted to form a glass, 
 (b) optionally, the molten glass is converted into a glass frit and the glass frit is melted to form a glass, 
 (c) the glass from step (a) or (b) is shaped into a glass blank, 
 (d) the glass blank is heat-treated at a temperature of 450 to 600° C. in order to form a glass blank with nuclei, 
 (e) the glass blank with nuclei is subjected to a heat treatment at a temperature of 600 to 850° C. in order to form a glass-ceramic blank with lithium metasilicate as crystal phase, or is subjected to a heat treatment at a temperature of 700 to 1000° C. in order to form a glass-ceramic blank with lithium disilicate as crystal phase, 
 (f) optionally, the glass-ceramic blank with lithium metasilicate as crystal phase from step (e) is subjected to a heat treatment at a temperature of 700 to 1000° C. in order to form a glass-ceramic blank with lithium disilicate as crystal phase, and 
 (g) optionally, in step (a) and/or (b) at least one chemical compound is added in order to change the chemical composition of the glass and/or of the glass frit. 
 
     
     
       2. Process according to  claim 1 , in which in step (a) residues of machined lithium silicate blanks are used. 
     
     
       3. Process according to  claim 1 , in which in step (a) blanks or residues of blanks of lithium silicate glass or lithium silicate glass-ceramic are used. 
     
     
       4. Process according to  claim 3 , in which the lithium silicate glass-ceramic is selected from lithium metasilicate glass-ceramic and lithium disilicate glass-ceramic. 
     
     
       5. Process according to  claim 1 , in which in step (a) blanks in the form of blocks, discs, or cylinders, residues of the blanks are used. 
     
     
       6. Process according to  claim 1 , in which in step (a) the blanks or residues of blanks and/or in step (b) the glass frit are melted at a temperature of 1200 to 1600° C., to form a glass. 
     
     
       7. Process according to  claim 1 , in which in step (a) the blanks or residues of blanks and/or in step (b) the glass frit is melted for a period of from 30 to 300 min, to form a glass. 
     
     
       8. Process according to  claim 1 , in which in step (c) the glass is shaped into a glass blank by pouring into a mould. 
     
     
       9. Process according to  claim 1 , in which the glass-ceramic blank prepared has lithium metasilicate or lithium disilicate as a crystal phase. 
     
     
       10. Process for the preparation of dental restorations, in which a glass-ceramic blank is prepared by the process comprising
 (a) lithium silicate blanks with different chemical composition or residues of lithium silicate blanks with different chemical composition are melted to form a glass, 
 (b) optionally, the molten glass is converted into a glass frit and the glass frit is melted to form a glass, 
 (c) the glass from step (a) or (b) is shaped into a glass blank, 
 (d) the glass blank is heat-treated at a temperature of 450 to 600° C. in order to form a glass blank with nuclei, 
 (e) the glass blank with nuclei is subjected to a heat treatment at a temperature of 600 to 850° C. in order to form a glass-ceramic blank with lithium metasilicate as crystal phase, or is subjected to a heat treatment at a temperature of 700 to 1000° C. in order to form a glass-ceramic blank with lithium disilicate as crystal phase, 
 (f) optionally, the glass-ceramic blank with lithium metasilicate as crystal phase from step (e) is subjected to a heat treatment at a temperature of 700 to 1000° C. in order to form a glass-ceramic blank with lithium disilicate as crystal phase, and 
 (g) optionally, in step (a) and/or (b) at least one chemical compound is added in order to change the chemical composition of the glass and/or of the glass frit, and 
 wherein the glass-ceramic blank prepared is given the shape of the dental restorations by pressing or machining. 
 
     
     
       11. Process of using the glass-ceramic blank prepared by the process according to  claim 1  for the preparation of dental restorations, comprising pressing or machining the glass-ceramic blank to form the dental restoration. 
     
     
       12. Process according to  claim 4 , in which the lithium silicate glass-ceramic is a lithium metasilicate glass-ceramic. 
     
     
       13. Process according to  claim 5 , in which the blanks are in the form of discs. 
     
     
       14. Process according to  claim 7 , in which the glass frit is melted for a period of from 30 to 240 min to form a glass. 
     
     
       15. Process according to  claim 9 , in which the glass-ceramic blank prepared has lithium metasilicate or lithium disilicate as main crystal phase. 
     
     
       16. Process according to  claim 1 , in which step (g) is also carried out. 
     
     
       17. Process according to  claim 6 , in which in step (a) the blanks or residues of blanks and/or in step (b) the glass frit are melted at a temperature of 1250 to 1450° C., to form a glass.